JP2000341061A - Switching noise reduction circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a switching noise reduction circuit that can properly suppress a switching noise with a simple configuration. SOLUTION: The switching noise reduction circuit is provided with a shift switch 1 consisting of 1st resistor groups comprising resistors 11, 12, 13 and of a 1st switch group comprising switches 14, 15, 16, a ladder switch 2 consisting of a 2nd resistor group comprising resistors 21, 22, 23, 24 and of a 2nd switch group comprising switches 25, 26, 27, 28, a signal amplification operational amplifier circuit 4 that receives a signal adjusted by the shift switch 1 and the ladder switch 2, and a capacitive element 3 that is provided to eliminate a high frequency component from the signal to be given to the signal amplification operational amplifier circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switch switching noise reduction circuit such as an integrated circuit for performing volume control of audio.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional volume control circuit. In FIG. 3, 1 is a shift switch, 2
Is a ladder switch, and 4 is a signal amplification operational amplifier circuit.

An audio signal input from a signal input terminal shown at the left end of FIG.
4, either switch 15 or switch 16 is ON
, Or all are OFF, four kinds of signal attenuation values can be obtained. Further, in the ladder switch 2, a desired signal attenuation value can be set by the number of the switches 25, 26, 27 and 28. The signal amplification operational amplifier circuit 4
The signal can be amplified.

Next, the operation in question will be described. For example, assuming that the switch of the shift switch 1 is switched, at the moment when the switch is switched, the electric charge in the switch constituted by the MOS transistor is discharged, which becomes noise. Since this noise potential is input to the + terminal of the operational amplifier 41, the noise is amplified and appears as a waveform at the output of the operational amplifier (a switch switching noise waveform according to the prior art shown in FIG. 2). This noise waveform is problematic because it can be heard as noise in response to hearing.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a switch switching noise reduction circuit capable of appropriately suppressing noise due to switch switching with a simple configuration.

[0006]

In a switch switching noise reduction circuit according to a first aspect of the present invention, a first resistor group including a plurality of resistors connected in series and a resistor in the first resistor group are connected. A first switch group consisting of a plurality of switches for adjusting the resistance value of the first resistor group by selectively opening and closing, and a plurality of resistors connected in series with the resistors of the first resistor group A second resistor group consisting of: a second switch group for adjusting the resistance value of the second resistor group by being selectively opened and closed by being respectively connected to the resistors in the second resistor group; A signal switch for receiving a signal adjusted by a shift switch including a first resistor group and a first switch group, and a ladder switch including the second resistor group and the second switch group. A flop circuit, is provided with a capacitor element to eliminate high frequency components of the signal to the signal amplifying operational amplifier circuit.

In the switch switching noise reduction circuit according to a second aspect of the present invention, the first resistor group including a plurality of resistors connected in series, and one end of the first resistor group as a common terminal. A first switch group consisting of a plurality of switches connected to the connection ends of the resistors in the resistor group, and a second resistor group consisting of a plurality of resistors connected in series to the other end of the first resistor group. A second switch group consisting of a plurality of switches having one end connected to the connection end of the resistor in the second resistance group and the other end connected in common;
An operational amplifier having a non-inverting terminal connected to the other end of the switch group, a resistor connected to an output terminal and an inverting terminal of the operational amplifier, and a resistor connected to a ground potential from the inverting terminal of the operational amplifier. One end is connected to the other end of the second switch group, and the other end is connected to the ground potential, and a capacitor element for eliminating a high-frequency component of an output signal is provided.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 shows an embodiment according to the present invention. In FIG. 1, a shift switch 1, a ladder switch 2, and a signal amplification operational amplifier circuit 4 are equivalent to those of the related art. 3 is a capacitor element. One end of the capacitor element 3 is connected to the output end of the ladder switch 2, the other end is connected to the ground potential, that is, the ground potential portion, and the signal amplification operational amplifier circuit 4 is connected to the output end of the ladder switch 2.

Reference numerals 11, 12, and 13 denote resistors constituting the shift switch 1, and reference numerals 14, 15, and 16 denote switches of a first switch group constituting the shift switch 1. These switches 14, 15, 16 are constituted by transmission gates using CMOS transistors. Switch 1
Reference numerals 4, 15, and 16 denote resistors 1 and 2 having one end, that is, an input terminal, of a first resistor group including resistors 11, 12, and 13 as a common terminal.
1, 12, and 13 are connected. That is,
The switch 14 is connected to one end of a first resistor group including the resistors 11, 12, and 13 and a connection end between the resistors 11 and 12, and the switch 15 is connected to a first end including the resistors 11, 12, and 13.
The switch 16 is connected to one end of the resistor group of the first resistor group and the connection end of the resistor 12 and the resistor 13, and the switch 16 is connected to the output side connection end of the resistor 13, that is, the other end of the first resistor group including the resistors 11, 12, and 13, that is, the output terminal. It is connected to the.

Reference numerals 21, 22, 23, and 24 denote resistors constituting the ladder switch 2, and reference numerals 25, 26, 27, and 28 denote switches of a second switch group constituting the ladder switch 2. These switches 25, 26, 27, 28 are CMOS
It consists of a transmission gate of a transistor. The switches 25, 26, 27, and 28 have one ends connected to the connection ends of the resistors 21, 22, 23, and 24 forming the second resistance group, and the other ends of the switches 25, 26, 27, and 28 are commonly used. The ladder switch 2 is connected to the other end of the shift switch 1 at one end, that is, the input terminal, and constitutes the other end, that is, the output terminal of the ladder switch 2. Here, the switch 25 has one end connected to the input-side connection end of the resistor 21 and the other end connected to the other end of the ladder switch 2, that is, the output end. The switch 26 has one end connected to the connection end of the resistors 21 and 22 and the other end connected to the other end of the ladder switch 2, that is, the output end. The switch 27 has one end connected to the connection end between the resistors 22 and 23 and the other end connected to the other end of the ladder switch 2, that is, the output end. The switch 28 has one end connected to the input-side connection end of the resistor 24 and the other end connected to the other end of the ladder switch 2, that is, the output end.

Reference numeral 41 denotes a + input terminal, that is, a non-inverting terminal, of the switches 25, 26, 2 of the second switch group.
The operational amplifiers which are connected to the output terminals of the signal amplification operational amplifier circuit 4 and which are connected to the output terminals of the signal amplification operational amplifier circuit 4, respectively. Here, the resistor 42 is connected to the output terminal of the operational amplifier 41 and the negative input terminal of the operational amplifier 41, that is, the inverting terminal. The resistor 43 is connected from a negative input terminal of the operational amplifier 41, that is, an inverting terminal, to a ground potential, that is, a ground potential portion. An output terminal of an operational amplifier 41 included in the signal amplification operational amplifier circuit 4 is connected to a signal output terminal shown at the right end in FIG. 1, and outputs the amplified signal to the outside.

Next, the operation will be described. Up to the point where the noise waveform is generated, it is equivalent to the conventional example. That is, the audio signal input from the signal input terminal shown at the left end of FIG. 1 first determines whether any one of the switches 14, 15, and 16 in the shift switch 1 is ON.
Alternatively, when all are OFF, four kinds of signal attenuation values can be obtained. Further, in the ladder switch 2, a desired signal attenuation value can be set by the number of the switches 25, 26, 27 and 28. The signal amplification operational amplifier circuit 4 can amplify a signal.

Here, for example, if the switch of the shift switch 1 is switched, the moment when the switch is switched, the MO
Discharge of the electric charge in the switch constituted by the S transistor occurs, and this becomes noise. Since this noise potential is input to the + input terminal of the operational amplifier 41, the noise is amplified and appears as a waveform at the output of the operational amplifier (a switch switching noise waveform according to the prior art shown in FIG. 2).

Although the generated noise waveform tends to enter the signal amplification operational amplifier circuit 4, the noise waveform is reduced by the effect of the capacitor element 3. Therefore, the noise waveform at the output terminal of the signal amplification operational amplifier circuit 4 has a small waveform value like the switch switching waveform of the present invention in FIG. Therefore, the noise waveform does not respond to hearing,
This has the effect of making noise inaudible.

The above operation has an effect that a noise waveform can be reduced. For example, a case where the switch 16 of the shift switch 1 switches from ON to OFF will be described as an example. At this time, the ladder switch 2
Only the switch 25 is ON and the others are OFF. The switch 16 is usually constituted by a transmission gate of a CMOS transistor, and the charge charged in the transmission gate when in the ON state is:
Released. The voltage fluctuation due to this release discharge is O
When the signal directly enters the input terminal of the P-amplifier, the output potential fluctuates instantaneously and appears as noise. In order to prevent the above, the capacitor element 3 is provided.

According to the first embodiment of the present invention, a first resistor group including a plurality of resistors 11, 12, and 13 connected in series, and one end of the first resistor group as a common terminal, The resistors 11, 12, and 13 in the first resistor group
A first switch group including a plurality of switches 14, 15, 16 that are respectively connected to the connection terminals of the first and second switches to selectively open and close to adjust the resistance value of the first resistor group; A second resistor group consisting of a plurality of resistors 21, 22, 23, and 24 connected in series with the other end of the first resistor group in the shift switch consisting of the group and the first switch group; Resistance 21 in the group,
A plurality of switches 25, 26, and 26, each of which has one end connected to the connection end of 22, 23, 24 and the other end commonly connected and selectively opened and closed to adjust the resistance value of the second resistance group. A second switch group consisting of 27 and 28; an operational amplifier 41 having a non-inverting terminal connected to the other end of the second switch group; a resistor 42 connected to an output terminal and an inverting terminal of the operational amplifier 41; A resistor 43 connected from the inverting terminal of the operational amplifier 41 to the ground potential.
And a capacitor element 3 having one end connected to the other end of the second switch group and the other end connected to the ground potential to eliminate a high-frequency component of an output signal to the operational amplifier 41. And a switch switching noise reduction circuit that can appropriately suppress noise due to the above with a very simple configuration.

[0017]

According to the first aspect of the present invention, the first resistor group including a plurality of resistors connected in series and the resistors in the first resistor group are connected to each other and selectively opened and closed. A first switch group consisting of a plurality of switches for adjusting a resistance value of the first resistor group, a second resistor group consisting of a plurality of resistors connected in series with the resistors of the first resistor group, A second switch group connected to the resistors in the second resistor group and selectively opening and closing to adjust a resistance value in the second resistor group; and a first switch group and a first switch. And a signal amplifying operational amplifier circuit for receiving a signal adjusted by the ladder switch comprising the second resistor group and the second switch group. Is provided with the capacitor element to eliminate the high frequency components, it is possible to obtain a switch switching noise reduction circuit which can appropriately suppress the noise due to switch switching in a simple configuration.

According to the second aspect, the first resistor group including a plurality of resistors connected in series, and one end of the first resistor group serving as a common terminal, the resistor in the first resistor group being used as a resistor. Of a plurality of switches connected to the connection terminals of
A second resistor group consisting of a plurality of resistors connected in series with the other end of the first resistor group;
A second switch group consisting of a plurality of switches having one end connected to the connection terminal of the resistor and the other end connected in common, and a non-inverting terminal connected to the other end of the second switch group. An operational amplifier, a resistor connected to an output terminal and an inverting terminal of the operational amplifier, and a resistor connected to a ground potential from the inverting terminal of the operational amplifier, and having one end connected to the other end of the second switch group. Since the capacitor element for eliminating the high-frequency component of the output signal connected to the other end and connected to the ground potential is provided, it is possible to obtain a switch switching noise reduction circuit that can appropriately suppress noise due to switch switching with a simpler configuration. .

[Brief description of the drawings]

FIG. 1 is a connection diagram showing a first embodiment according to the present invention.

FIG. 2 is a curve diagram showing switch switching waveforms in the embodiment according to the present invention and the prior art.

FIG. 3 is a connection diagram showing a volume control circuit according to the related art.

[Explanation of symbols]

1 shift switch, 2 ladder switches, 3 capacitor elements, 4 signal amplification operational amplifier circuits, 11, 12,
13 resistance, 14, 15, 16 switch, 21, 22
2, 23, 24 resistors, 25 switches, 41 operational amplifiers, 42, 43 resistors.

Claims (2)

[Claims] A first resistor group including a plurality of resistors connected in series; and a resistor in the first resistor group connected to and selectively opened and closed by resistors in the first resistor group. A first switch group consisting of a plurality of switches for adjusting a value, a second resistor group consisting of a plurality of resistors connected in series with the resistors of the first resistor group, and a resistor in the second resistor group. A second switch group connected to the second resistor group to adjust a resistance value of the second resistor group by being selectively opened and closed; a shift switch composed of the first resistor group and the first switch group; A signal amplifying operational amplifier circuit for receiving a signal adjusted by a ladder switch including a second resistor group and a second switch group, and eliminating a high-frequency component of a signal to the signal amplifying operational amplifier circuit. 1. A switch switching noise reduction circuit, comprising: a capacitor element to be removed. 2. A first resistor group consisting of a plurality of resistors connected in series, and one end of the first resistor group connected to one end of the first resistor group as a common terminal. A first switch group consisting of a plurality of switches, a second resistor group consisting of a plurality of resistors connected in series with the other end of the first resistor group, and a connection of the resistors in the second resistor group. A second switch group consisting of a plurality of switches having one end connected to one end and the other end connected in common;
An operational amplifier having a non-inverting terminal connected to the other end of the switch group, a resistor connected to an output terminal and an inverting terminal of the operational amplifier, and a resistor connected to a ground potential from the inverting terminal of the operational amplifier. A switch switching noise reduction circuit, comprising a capacitor element having one end connected to the other end of the second switch group and the other end connected to a ground potential to eliminate a high-frequency component of an output signal.